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Small plastic particles, known as microplastics, are of increasing concern for marine and freshwater species. Microplastics have been reported globally in a wide range of marine species including mussels, crabs, fish and seabirds. This was the first study to investigate microplastic accumulation in the New Zealand green-lipped mussel, Perna canaliculus. This thesis investigated microplastic accumulation in the New Zealand green-lipped mussel and the effects of microplastics, both singly and in combination with triclosan (a hydrophobic, anti-microbial compound), on the green-lipped mussel.

Microplastic accumulation in green-lipped mussels around New Zealand was investigated using a field survey whereby mussels were collected from eight mussel beds around New Zealand with a more in depth survey conducted in Canterbury. Mussels were acid digested and the resulting digests observed under fluorescence coupled microscope to identify potential microplastic particles. Across both National and Canterbury mussel surveys, 35% of mussel samples analysed contained microplastics, the majority (78%) of the plastics isolated were fragments, with fibres (13%) and beads (9%) also located.

Microplastics can sorb hydrophobic contaminants from the water, potentially providing an additional pathway of exposure of marine species to contaminants. An acute 48 h laboratory study was conducted to investigate the effects of microplastics and triclosan, both individually and combined, on green-lipped mussels. The range of biomarkers assessed included clearance rate, oxygen respiration rate, byssus production, superoxide dismutase (SOD) activity, glutathione-S-transferase (GST) activity and lipid peroxidation. Microplastics had adverse effects on mussel physiology including decreased oxygen respiration rate and byssus production when present alone. These physiological impacts were not observed when the microplastics were sorbed with triclosan. Triclosan, both alone and with microplastics, adversely affected mussel oxidative stress markers including SOD activity and lipid peroxidation. A potential synergistic effect was observed on the SOD enzyme activity when mussels were exposed to triclosan sorbed to microplastics. No effect on the biochemical biomarkers was observed for mussels exposed to microplastic only. Microplastics enhanced the uptake of triclosan in the mussel tissue when triclosan was sorbed to microplastics compared with triclosan in the absence of microplastics. This indicates that microplastics potentially provide an additional pathway of exposure of hydrophobic contaminants to mussels in the marine environment.

This research illustrates that green-lipped mussels accumulate microplastics in the New Zealand marine environment. If concentrations of microplastics in the marine environment continue to increase, adverse effects on mussel physiology and uptake of sorbed contaminants may occur.